U.S. Pat. No. 4,376,318 to Cirillo discloses a portable playpen wherein the foldable playpen includes upper and lower retaining frames separated by vertical members. The end or side of the vertical structure members fold inwardly and released vertical members to provide a compact arrangement for carrying.
U.S. Pat. No. 4,837,875 to Shamie et al. discloses a folding playpen with attached fabric enclosure. A playpen includes a frame having floor supports with inner ends which are connected to each other by a hub that permits swinging of the floor supports in a horizontal plane from an in use position to a folded position. The uprights are connected by hinges to the outer ends of the floor supports. Bendable sides and end rails interconnect the tops and bottoms of the uprights. One of the cross-members can be removed whereas provided with a mechanism to permit its elongation, such that the frame can be folded with all other parts permanently connected to each other and without removing the fabric enclosure.
U.S. Pat. No. 4,070,716 to Satt et al. discloses a foldable playpen having two end portions and two side portions which are interconnected to form a substantially square frame. The two end portions are pivotal in a downward direction toward a center vertical leg located at each end and the side portions are pivotal inward bringing the two folded end portions together, to thereby fold the playpen.